| 摘要 |
Process for preserving the dyeing capacity of 5,6-dihydroxyindole or of of its derivatives corresponding to the formula (I);in which R1, R2, R3 and R4, which are identical or different donates hydrogen or a C1-C4 lower alkyl, R1, R2 and R3 denoting hydrogen when R4 denotes alkyl in an aqueous medium, characterized in that the pH of the aqueous medium is adjusted to a value pHC of between 5 and 10 by employing a pH-regulating agent containing two components (A) and (B), the component (A) being chosen from pH-regulating agents which have a dissociation constant KCA in aqueous solution at 25° C., such as pkCA, that is:and the component (B) being chosen from pH-regulating agents which have a dissociation constant KCB in aqueous solution at 25° C., such as pkCB, that is:
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